The present invention relates to a semiconductor device, and more particularly to techniques which are effective when applied to a resin-encapsulated semiconductor device.
Further, the present invention relates to techniques for preventing the appearance of cracks in an electron device, especially a resin-molding package. The techniques are effective for, for example, a semiconductor integrated circuit device (hereinbelow, termed "IC") which is furnished with a surface-packaging plastic package.
As regards a semiconductor chip having a built-in DRAM (Dynamic Random Access Memory), it is the mainstream to mold the chip in the form of a resin-encapsulated semiconductor device of the SO (Small Out-line) type. The resin-encapsulated semiconductor device of this sort belongs to the so-called flat packaging type. The resin-encapsulated semiconductor device is such that a tab portion, the semiconductor chip mounted on the tab portion, and inner leads are molded in a resin. Each of outer leads is in the shape of a J-bend which protrudes out of a resin mold member and which extends to the lower surface of this resin mold member. The external terminals (bonding pads) of the semiconductor chip are connected to the inner leads through pieces of bonding wire. The resin mold member is formed of an epoxy type resin.
The resin-encapsulated semiconductor device thus constructed is installed on a printed-wiring circuit board by a vapor-phase reflowing process. In the vapor-phase reflowing process, a solder is deposited on both the printed-wiring circuit board and the outer leads of the resin-encapsulated semiconductor device in advance. Subsequently, a heat treatment is carried out in an atmosphere of dichlorodifluoromethane at about 230 [.degree. C.] for about 90 [sec], whereby the solder is melted to connect the outer leads of the resin-encapsulated semiconductor device to the printed-wiring circuit board.
In addition, the tab portion is held connected to the frame portions of a lead frame through tab suspension leads before the step of cutting and molding the lead frame. Each of the tab suspension leads has one end side connected to the center of the shorter latus of the oblong tab portion, and has the other end side connected to the position of the frame portion of the lead frame discrepant from the central part thereof. That is, the central part of the tab suspension lead is in a shape similar to the shape of a crank so that the other end side of the tab suspension lead can be connected to the position discrepant from the central part of the frame portion. In a case where, at the step of pouring a resin, an inflow port (resin gate) for the resin is arranged centrally of the shorter latus of the tab portion, the other end side of the tab suspension lead is located so as not to agree with the position of the resin gate. In a case where the positions of the two are in agreement, the cracks of the resin mold member ascribable to a cutting tool appear frequently when the resin at a part corresponding to the inflow port is cut at the step of cutting and molding the lead frame. The inflow port for the resin is arranged at the central part of the shorter latus of the tab portion so as to bring the extending direction of the pieces of bonding wire and the inflowing direction of the resin into agreement lest the bonding wire pieces should be short-circuited by the inflow of the resin.
This resin-encapsulated semiconductor device of the SO type is described in, for example, "VLSI DEVICE HANDBOOK" issued by Kabushiki-Kaisha Science Forum on Nov. 28, 1983, pp. 221-231.
In addition, a certain IC for realizing a high density of packaging is furnished with a resin-molding package which is so constructed that the plane area of a tab with a pellet bonded thereto is comparatively large (for example, 5 mm-square or above), so outer leads are surface-packaged.
By the way, an example of literature containing such an IC is "IC IMPLEMENTATION PACKAGING TECHNOLOGY" issued by Kabushiki-Kaisha Kogyo Chosa-Kai on Jan. 10, 1980, pp. 135-155.